1. Field of the Invention
The present invention relates to an image display apparatus such as, for example, a viewfinder or a projection-type video projector, which is equipped with an image display device of a matrix display system.
2. Description of the Prior Art
An image display apparatus equipped with an image display device (hereinafter referred to as a matrix display device) such as, for example, a liquid crystal display panel, capable of accomplishing a matrix display is generally so designed as to present a viewable image by selectively turning on a plurality of dot-like display segments. Where a particular color filter array is employed for each picture element of the matrix display device, a color image can be displayed.
As a specific example of the image display device capable of accomplishing a matrix display, reference will now be made to the liquid crystal panel. FIG. 29 illustrates a sectional representation of the standard transmission-type liquid crystal display panel 4 and FIG. 30 illustrates a plan view thereof. The liquid crystal display panel 4 includes a first transparent insulating substrate 11 having an inner surface formed with a plurality of transparent pixel electrodes 12 and a matrix array of switching electrodes such as thin-film transistors 13 which are non-linear elements and which are connected respectively with the pixel electrodes 12. The liquid crystal display panel 4 also includes, as shown in FIG. 30, a matrix array of source bus electrodes 14 and a matrix array of gate bus electrodes 15, both for supplying a voltage to sources and gates of the switching electrodes 13.
A second transparent insulating substrate 16 disposed in face-to-face relationship with the first transparent insulating substrate 11 has an inner surface deposited with a common electrode 17 and color filters 18a and 18b arranged in a pattern similar to the pattern of the pixel electrodes 12. The inner surface of the second transparent insulating substrate 16 is also formed with light shielding layers 19a and 19b corresponding in position to the switching electrodes 13 and the bus electrodes 14 and 15, respectively, each of the light shielding layers being disposed between each neighboring color filter 18a and 18b. A layer of liquid crystal 20 is sealed within a space delimited between the first and second transparent insulating substrates 11 and 16.
A first polarizing plate 21 is disposed on an exit side of the liquid crystal display panel 4, for example, on an outer surface of the first transparent insulating substrate 11, while a second polarizing plate 22 is disposed on an incident side of the liquid crystal display panel 4, for example, on an outer surface of the second transparent insulating substrate 16.
In the liquid crystal display panel 4 of the above described construction, since the switching electrodes 13 and the various bus electrodes 14 and 15 are opaque, no light passes therethrough. In other words, only areas surrounded by the bus electrodes 14 and 15 form light transmitting windows 23 and, of these light transmitting windows 23, only the areas excluding the switching electrodes 13, that is, only the pixel electrodes 12 and spaces surrounding the pixel electrodes 12, form effective areas through which light can pass. When the matrix display device represented by such a liquid crystal display panel is employed in a projection-type projector and an image is then projected by the projector on an enlarged scale or an image is then viewed through a viewfinder system on an enlarged scale, the picture elements tend to be visually noticeable in the form of a pattern of discontinuous dots and, therefore, the quality of the image projected or viewed is considerably reduced.
In view of the foregoing, and in order to minimize a reduction in image quality resulting from the presence of the switching electrodes 13 and the various bus electrodes 14 and 15, the Japanese Laid-open Patent Publication No. 3-148622, published Jun. 25, 1991 (claiming priority based on U.S. Ser. No. 382,514 filed Jul. 20, 1989) suggests the use of a diffraction grating disposed on a front side, i.e., a location closer to the viewer's eye, of the liquid crystal display panel to provide a blurring phenomenon in an optical system. However, this prior art technique has a problem in that, since no relationship among the spatial cut-off frequency, the Nyquist frequency and the sampling frequency is taken into consideration, the contrast of the image tends to be lowered thereby failing to provide a sensation to a high resolution.